This invention relates to an air conditioning system for an aircraft, and more particularly, the invention relates to a pneumatic cabin super charger.
Aircraft engine designs typically employ bleed ports that pipe air to air supply systems or bleed systems that provide compressed air to an air conditioning system. An environmental control system (ECS) distributes the conditioned air throughout the aircraft. In the 1960""s the Convair 880 utilized a super charger having a single compressor and a single turbine to provide compressed air for the air conditioning system.
Typically, one of the engine bleed ports provides fan air to cool the bleed air supplied to the air conditioning system. An intermediate pressure bleed port provides air for the air conditioning system to ventilate and cool the aircraft cabin during normal flight. A high pressure bleed air port ventilates and cools the aircraft cabin during ground idle and aircraft descent. The intermediate pressure bleed port location is typically located on the engine such that sufficient air pressure is provided for a scenario referred to as xe2x80x9chot day, end of cruisexe2x80x9d, which simulates a worse case scenario for aircraft ventilation. As a result, the intermediate pressure bleed port exceeds the ECS pressure requirements during a typical standard day cruise.
Typically, the ECS only requires approximately 30 psi of air pressure. At the standard day cruise condition the bleed port provides a pressure much higher than 30 psi, sometimes as much as 40-90 psi, and a pressure regulator must be employed to throttle the intermediate pressure bleed air to the desired air pressure.
As a result, bleed air is provided at a much higher pressure than is typically required and the engine efficiency is reduced. Other alternatives have been proposed to increase the efficiency of the engine such as taking air from the lower pressure sections of the engine compressor. However, such alternatives are not feasible because the compressor sections typically contain variable geometry and guide vanes that make such a system undesirable. Therefore, what is needed, is an air conditioning system and super charger that reduces the air pressure bled from the engine and increases overall engine efficiency.
The present invention provides an aircraft air conditioning air supply system including a primary propulsion turbine engine having a bleed valve providing pressurized air. A ram air inlet provides ram air. A super charger includes a spool with at least two turbines mounted thereon driven by the pressurized air from the engine. At least one compressor is connected to the turbines, preferably mounted on the same spool as the turbines, and receives the ram air. The turbines drive the compressor and compresses the ram air for use by an air conditioning pack. The supercharger provides compressed air to the air conditioning pack. The air conditioning pack provides refrigerated air that is distributed throughout the aircraft.
The number of turbines and compressors for the super charger is selected by matching the specific speeds of the compressors and turbines. The specific speed is indicative of the efficiency of the compressor and turbine and provides an overall efficiency of the super charger. Of course, the number of turbines and compressors dictates the cost of the super charger and is balanced against the increased efficiency from the engine due to the reduced amount of bleed air required for the super charger.
Accordingly, the above invention provides an air conditioning system and super charger that reduces the air pressure bled from the engine and increases the overall engine efficiency.